1. Field of the Invention
The present invention relates to a method of fabricating a display device having a stacked structure of thin films. More specifically, the invention relates to the step of forming an opening in a thin film in the process of fabricating a display device.
2. Description of the Related Art
Thin film transistors (also referred to as “TFTs”) and electronic circuits having TFTs are fabricated by the steps of stacking various thin films such as a semiconductor film, an insulating film, and a conductive film, and forming predetermined patterns in the films by a photolithography technique as appropriate. A photolithography technique is a technique of transferring a circuit pattern or the like, which is called a photomask and is formed from a non-light-transmissive material on a transparent flat plate, onto a substrate through light exposure, and is widely used in the process of fabricating semiconductor integrated circuits and the like.
A fabrication process of a semiconductor device using a conventional photolithography technique involves a number of steps such as light exposure, development, baking, and peeling for the process of handling a mask pattern which is formed from a photosensitive organic resin material called photoresist. Therefore, the more the number of photolithography steps is increased, the more the fabrication cost is inevitably increased. In order to overcome such drawbacks, a fabrication process of TFTs with a reduced number of photolithography steps has been studied (e.g., see Reference 1: Japanese Published Patent Application No. 2000-133636). In Reference 1, a resist mask formed by photolithography steps which is used once is subjected to cubical expansion by swelling treatment so that the mask can be used again.